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Here's Why Hurricane Joaquin Is So Inscrutable


Joaquin is churning through the Atlantic and may hit the U.S. coastline over the next four days or maybe not. The models forecasting this hurricane's path diverge widely. They point to landfall in Georgia, in the mid-Atlantic, around the District of Columbia or not at all. Jeff Halverson is a meteorologist who teaches at the University of Maryland, Baltimore County, and he joins me now to explain why Hurricane Joaquin is proving so difficult to analyze. Welcome to the program.

JEFF HALVERSON: It's great to be here.

SIEGEL: First, I mean, roughly how many big models are there, and how divergent are they?

HALVERSON: There's quite a few models that the Hurricane Center uses. There are two heavy players - what we call the Global Forecast System, which is the American model, and the European Centre for Medium-Range Weather Forecast, or the ECMWF. Those are the two big players.

SIEGEL: And they have quite different forecasts of where the storm is heading, those two big ones.

HALVERSON: They've had different forecasts for several days. However, today, they're actually starting to come in to some agreement.

SIEGEL: Really? What's the consensus?

HALVERSON: Well, the consensus seems to be shifting the track of the storm - the most likely track - further and further east away from the DC-Baltimore region and perhaps more to a concern, let's say, from New Jersey, from New York City up through Boston.

SIEGEL: Now, would that mean that the Europeans have had this one a bit more right than the American model to date?

HALVERSON: Well, the European model has had some remarkable consistency on this. It has basically maintained all along that the storm is going to stay further to the east than many of the other models.

SIEGEL: But isn't everyone who's forecasting this and has a model for it - aren't they all using the same data provided by the U.S. government?

HALVERSON: The data is very similar, but the way that these models are formulating it is - or constructed - very, very different. There are different scientific teams that put these models together. There are different assumptions that are made about what physics to keep in, what physics to keep out. And you know, it's a trade-off. The more physics you put in, the more accurate the model, but it would take much, much longer to run. So you trade accuracy of the physics versus the efficiency of computation.

SIEGEL: Hurricane Sandy, I guess, where it hit the East Coast of the U.S. - that was much more in keeping with the European model - wasn't it? - than with the American model?

HALVERSON: Well, the European - that was a dead ringer for five, six, even seven days before that storm made that infamous left hook. The European never wavered from that solution, and that's why it gained such a reputation.

SIEGEL: After the American model did not gain that - quite that reputation, there was talk of really beefing up weather tracking and forecasting. Did that happen?

HALVERSON: That's in the progress. There's a - Congress has released what's called Sandy Stimulus Funding, a lot of the money went to NOAA, the weather service, to beef up the computational speed and efficiency of the American models. But you know, in all fairness, the ECMWF has had its share of flaws. It has missed some significant storm events. It's not the silver bullet. It's not the perfect model. And that's the challenge to meteorologists. That's the art of interpreting all this guidance in front of you. You have to really know what are the strengths and weaknesses of each individual model. Some models do better in winter. Some do better in summer. And that is where the human interpretation is so vital.

SIEGEL: OK, thanks. Jeff Halverson is a meteorologist with The Washington Post's Capital Weather Gang and he's on the faculty of the University of Maryland, Baltimore County. Thanks for talking with us.

HALVERSON: It's been a great pleasure. Thanks. Transcript provided by NPR, Copyright NPR.